1. Field of the Invention
The current invention relates to an exercise device for monitoring body parameters of a wearer during exercise. The invention also relates to sensor for determining sensor signals from which body parameters can be derived and to a method of determining body parameters during exercise.
2. Background Information
To achieve fitness goals it is necessary to exercise in the right intensity. Heart rate is one of the most accurate measurements of the intensity or exertion level of an exercise workout. The fitness of the heart is the key to aerobic endurance. Aerobic endurance is extremely important for both general fitness training and professional athletes. Heart monitors are one of the most effective aids for tracking and developing the progress on the path to increased aerobic endurance. For example, to loss weight and burn fat, it is desirable to exercise at 60-70% of one's maximum heart rate. To improve cardiovascular fitness, it is more suitable to exercise at 70-80% of one's maximum heart rate. Exercise at the wrong intensity will just waste the effort or may even harm the body.
Heart rate can easily be checked by checking the pulses at the wrist manually for, say, 15 seconds during exercise and calculate beats per minute. However, stopping during exercise to count pulse is not only inconvenient, but also disrupts both the workout and the heart rate. This method also introduces pressure to the carotid artery which slows down the pulse. Electronic heart monitors are an effective way to track and record heart rate over the course of an entire workout. They not only provide a complete record of the heart rate for the duration of your workout, but they are also more accurate than manual methods, and can provide other information such as body temperature, SpO2 (Oxyhemoglobin saturation by pulse oximetry) are also important information to determine condition of the body.
For professional athletes, cardiovascular fitness is the most significant factor in speed. Measuring the work-rate of the heart is one of the most accurate methods of determining how much benefit an athlete derives from a workout. A heart rate monitor can also help to avoid stressing the body too much. They are a useful tool for maximize the efficiency of the training while minimizing the opportunity for injury. Heart rate monitors also enable professional athletes to exercise below a certain ceiling, i.e. avoid depleting the body's glycogen stores and ensuring that the body has the energy to perform intense workouts with vigor. For general fitness training, a heart rate monitor can function as a coach guiding the user when he or she can handle more and work harder.
Most popular heart rate monitors use ECG type chest belt with a wireless link to sports watch. The heartbeat is detected by sensing the ECG signal from the chest belt and a pulse is sent to the sports watch via wireless connection. This type of heart rate monitor is accurate and reliable, but has the disadvantage that it is not comfortable for the user to wear a plastic belt on the chest during exercise. The belt will also become very dirty after use. Another method of detecting heartbeat is to use IR LED and IR sensor through the ear lobe or finger tip. This type of detector has the intrinsic problem of motion artifact and they are simply not reliable during exercise.
There are many devices that can measure body parameters of a person. For example, by using an infrared ear thermometer, clinical thermometer, the user could get his body temperature and by using pulse oximeter the user could get his heartbeat and the amount of oxygen attached to the hemoglobin. However, none of these devices is suitable for continuous monitoring of the body parameter when the user is doing exercise. The thermometer, for example, is not suitable for use in motion. For finger pulse oximeter, study suggested the motion will result in blood volume changes that invalidate its measurement [ref—“Motion Artifact in Pulse Oximetry”, M. R. Neuman and N. Wang, Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Vol. 12 No. 5, 1990].
FIG. 1 is a schematic illustration is a typical finger type pulse oximeter implementation. Measuring heartbeat rate and SpO2 (blood oxygenation) is based on the absorption of red and infrared light. The technology is very sensitive to motion and hence is generally not suitable for use in personal exercise monitors. A few mechanical designs attempt to improve motion tolerance and enable the measurement to be used later in signal processing such that the heart rate in addition to SpO2 can be derived when the wearer is in motion. The device comprises two light sources, typically using LEDs of known wavelength. The wavelengths of the two light sources are 880-920 nm (Infrared or IR) and 660 nm (Red) respectively. To obtain heart rate (HR) only the IR light source is needed. To calculate blood oxygen levels (pulse oximetry) both the Red and the IR LED's would need to be used. In either case a photo detector is used to sense the light that has been transmitted or reflected into the skin or application sight. This transmission of light into an area of the body that is carrying blood and reflected back to the photo detector will be effected by the pulsiltile flow caused by each heartbeat. This slight change in light intensity is detected and extracted to create a waveform commonly known as a plethysmograph. This waveform or the actual detection of the pulsiltile flow can be converted into heart rate in the absent of motion. To calculate pulse oximetry the IR and the red light emissions are separately analyzed and then used in an empirical calculation to generate a predetermined blood oxygen level. The calibration and empirical calculation can be found in many literatures.
FIG. 2 shows an example of noise induced by motion in an IR LED and IR heartbeat/SpO2 sensor. This noise signal may be of similar or even larger amplitude than the heartbeat signal and they are, in normal situation, in the same frequency band of the heartbeat signal (1-3 Hz). There is no easy method to extract the heartbeat signal from the mixture of the motion signal and heartbeat signal.